(1) Field of the Invention
The present invention relates to an erasable ink the lines drawn with which can be erased with an eraser.
(2) Description of the Related Art
An erasable ink the lines drawn with which can be erased with an eraser is disclosed in, for example, Japanese Patent Application Laid-Open No. Sho 59-223769 as "an erasable ink composition characterized by dispersing homogeneously a pigment selected from carbon black and aniline black in a water base medium dissolving polyethylene oxide in the presence of a surfactant containing a polyoxyethylene group". In this erasable ink, however, the erasability itself is not satisfactory and in particular, erasing after a long lapse of time is difficult. In addition to the above, erasable inks having various compositions have been proposed, but they have insufficient erasability and have not yet provided desired effects.
The present applicants disclosed in Japanese Patent Application Laid-Open No. Hei 7-56090, "an erasable ink characterized by containing a resin having a glass transition temperature of 0.degree. C. or lower, colored spherical fine particles and water". However, lines drawn with this erasable ink on non-absorbing surfaces of glass, plastics and metals and surfaces of writing materials such as wood free paper can be erased well with erasing tools such as an eraser. In contrast with this, when lines are drawn on paper having a relatively coarse surface, a coloring component contained in the ink remains on the writing material because of the insufficient adherence of a pigment component used for a colorant to a binder resin which is a binding component for the colorant, and therefore the drawn lines can not completely be erased.
In the case where the erasable ink is charged into writing tools such as felt tip pens and ball point pens, the coloring component of the ink separates and settles down in the pen bodies after a long lapse of time because of the large particle size thereof. Accordingly, the storage stability grows worse, so that the concentrations of the coloring component and the resin component of the ink running out of the pen point are reduced, and therefore the writing performance is deteriorated. Further, there is the defect that the ink is liable to be dried at an ink flowing part of the pen body because of an emulsion resin of a high concentration contained in the ink. In the case where the ink is charged into an ink tank comprising an ink absorber such as cotton, there is caused the problem that it is difficult for the ink to flow smoothly because of the high viscosity thereof.